Amphoteric modified vermiculites as adsorbents for enhancing removal of organic pollutants: Bisphenol A and Tetrabromobisphenol A.

Three novel organic vermiculites (VER) modified by amphoteric surfactants (BS, SB and PBS) with different negatively charged groups (carboxylate, sulfonate and phosphate) were demonstrated and used for removal of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA). The difference in the structure and surface properties of modified vermiculites were investigated using a series of characterization methods. BS and SB surfactant mainly adsorbed on the surface and hard to intercalate into the interlayer of VER, while both adsorption and intercalation occurred in PBS modification. This difference resulted in different packing density of surfactant and hydrophobicity according to the results of contact angle, and affect the adsorption capacities ultimately. The adsorption of two pollutants onto these modified vermiculites were very fast and well fitted with pseudo-second-order kinetic model and Langmuir isotherm. PBS-VER exhibited the highest adsorption capacity (92.67 and 88.87 mg g-1 for BPA and TBBPA, respectively) than other two modified vermiculites in this order PBS-VER > BS-VER > SB-VER. The ionic strength (Na+, Ca2+) and coexisting compounds (Pb2+, humic acid) have different effects on the adsorption. PBS-VER had a good reusability and could remove ionic (methylene blue and orange G) and molecular (BPA) pollutants simultaneously and effectively due to the function of amphoteric hydrophilic groups and alkyl chains. The results might provide novel information for developing low-cost and effective adsorbents for removal of neutral and charged organic pollutants.